Scuba diving is more than a sport. It's a science that operationally
integrates physics, chemistry, physiology, and oceanography. It's also
pretty cool.

Begin the lesson by showing students a can of compressed air. "Air blasters"
are often available as commercial dusting sprays at photographic supply
stores. Explain that the can contains a large volume of air that has been
compressed into a small space. Within this space, the gas is stored under
considerable pressure. When the nozzle is pressed, some of the pressurized
gas escapes from the can.

Attach a length of plastic tubing or a nozzle extension to the
can. Press the nozzle to demonstrate the directional flow of air. Fill
a fish bowl with water. Position the free end of the tubing beneath the
water's surface. Press the nozzle and have students observe the rush of
rising air bubbles.

Challenge the class to critically analyze their observations.
What causes the rush of bubbles? What do the bubbles contain? Predict how
much air is stored in the can. Can compressed air support living things
that require oxygen?

Scuba-from the phrase "self-contained underwater breathing apparatus"-refers
to a type of diving in which an individual carries his or her own supply
of air. This air supply is stored within a steel or aluminum cylinder called
a scuba tank. A device called a regulator "taps" the pressurized air and
adjusts its flow for breathing.

Prior to the dive, a mechanical compressor fills the tank with a large
volume of air. The pressure produced by this compressed air can exceed
200 times the standard atmospheric pressure! As a diver breathes, flow-adjusting
devices called stages drop the flow pressure. Air that is exhaled does
not return to the scuba tank. Instead, it is released and observed as the
rush of rising bubbles. Sport divers can safely dive to a depth of about
39 meters (130 feet) or five atmospheres of pressure.

Although the first crude scuba apparatus was invented over 150 years
ago, it was Jacques-Yves Cousteau and Emile Gagnan who perfected the modern
day Aqua-Lung. Unlike the "hard-hat" divers that relied on a surface air
hose, Cousteau (in the early 1940s) had attained untethered freedom.

1. Suppose a balloon filled with air was released from the sea bottom.
How does the surrounding pressure change as the balloon rises? What is
likely to happen to the balloon before it reaches the surface? Explain.

2. The bends is a life-threatening illness that results from too
rapid a return to surface air pressure. During ascent, nitrogen dissolved
in the blood stream comes out of solution as lung bubbles that can block
the flow of blood to critical body organs. When construction of underwater
foundations for the Brooklyn Bridge was underway, laborers worked in pressurized
chambers. Upon a rapid return to the surface, many suffered from the bends.
If you were in charge of this construction project, how might you protect
these workers from decompression sickness?

UPS AND DOWNS OF DIVINGSCUBA DIVING: Student Activity
Create a Cartesian diver and watch what happens when
you put it under pressure

Imagine entering a freshwater pond or lake. Take a deep breath
and you're likely to float. Exhale, and you'll probably find yourself sinking.
These "ups and downs" depend upon the amount of air in your lungs. As the
volume of this gas increases, you become more buoyant. As the gas volume
drops, you lose buoyancy and begin to sink.

In this main activity, you'll construct a device called a Cartesian
diver. Like a floating person, this diver has a buoyancy that depends upon
its volume of trapped air. As you explore its behavior, you'll uncover
the relationship between pressure and volume.

Materials

plastic 1- or 2-liter soda container with a screw-on lid

glass medicine dropper

1. Fill
the container with tap water.

2. Lower the medicine dropper into the container. Squeeze the
bulb slightly so that the glass tube becomes partially filled with water.

3. Set the dropper floating within the container. Add more water
to the container so that the level of water rises to the brim.

4. Screw on the container lid. The seal should be tight enough
to prevent the leakage of water.

5. Squeeze the center of the plastic container. What happens to
the medicine dropper? Release your pressure. What happens now? Note: If
the dropper remains afloat, you'll need to open the container and fill
the dropper tube with more water.

6. Take a close look at the air bubble trapped within the medicine
dropper. What happens to the bubble's volume as you squeeze the container?
Can you explain the connection between this change in volume and the behavior
of the medicine dropper? What happens to the bubble's volume when you release
your grip? How does a change in volume relate to the movement of the medicine
dropper?

Extend the activity

Can you modify the design of your medicine dropper so that it
can recover items that are scattered at the bottom of the container? First,
design a diver that can retrieve paper clips and other objects attracted
to magnets. Then, redesign your diver to "recover" targets that have eyelet-like
handles.

Is it possible to make a Cartesian diver out of other materials, such
as the plastic cap to a pen, weighted with a bit of clay? See what objects
will work.

Questions

1. Does squeezing the bottle force more water into the air or
compress the air, making the diver heavier and causing it to sink?

2. How do these demonstrations relate to scuba diving equipment?
How do they explain free divers' use of stones for weight as they dive?

Our featured contributor
is the National Association of
Black Scuba Divers (NABS) (800) 521-NABSwww.nabsdivers.org

Contact a local
dive shop and invite one of the divers to visit the class. Ask the diver
to bring and demonstrate the proper and safe use of scuba equipment.

Put on a pair
of safety goggles. Then, pour a small amount of vinegar into a small beverage
container. Place about a teaspoon of baking soda into a balloon. Slip the
neck of the balloon over the neck of the bottle. Pick up the balloon so
that the baking soda falls into the vinegar. Observe what happens to the
balloon as the pressure within the container increases. Can this observation
be applied to diving? If so, how?

Research the
depth limits associated with scuba diving. Why can't divers descend past
a certain depth? How can dolphins and whales dive to incredible depths
while scuba divers are restricted to the near surface waters?

NEWTON'S APPLE video cassettes and educational materials
provide further information about this and other topics. Call 1-800-588-NEWTON.